The technology disclosed relates to methods and systems that can be used to reduce visible artifacts know as mura. In particular, it relates to producing alignment marks by physically modifying appearance of a layer of exposure or radiation sensitive material on a workpiece, then using those alignment marks or transferred direct or inverted images of those marks to realign a writing coordinate system between exposure writing passes, following physical movement of the workpiece within the writing system. The physical modifications described include mechanically pressing a mark into the layer, using a laser to ash or ablate the layer, or applying an ink or other substance to the surface of the laser.
Prior alignment systems often have involved precisely placed marks added to substrates by a substrate manufacturer, such as holes drilled in the substrates. These marks would need to be detected through one or more layers of exposure sensitive and other materials applied over the mask substrate. A wide range of mark types added to reticles, masks and other workpieces have been described. Typically alignment marks have been added lithographically in the first layer exposed onto the substrates. A variety of optics for alignment have also been described.
An opportunity arises to supply better alignment systems for writing small features, especially better alignment systems for large area masks. Better masks that produce less visible artifacts may result.